Different types of fluid level measuring systems are know in the prior art. For example, U.S. Pat. No. 6,202,486 is directed to an analog liquid level sensor for determining the location of the surface of liquid in a container. The sensor includes a hollow tubular stainless steel probe inserted into the container and having thermocouples operatively arranged within the probe to sense temperature above the liquid surface and beneath the liquid surface. Resistance of a wire within the probe together with temperature readings are used to determine the liquid level in the container.
U.S. Pat. No. 4,566,322 teaches an apparatus for electronically measuring the level of a liquid in a container, and particularly the level of gasoline in the gasoline tank of a vehicle. The device includes a conductor foil enclosed by a protective tube, the conductors of which form a temperature-dependent, externally heated resistor or electrodes of a measurement capacitor, and a conductor-foil support that is divided into three rigid sections every two of which are pivotally connected together in the manner of a toggle joint and being under spring tension in such a manner that the outermost section can rest against the bottom and the top side of the container.
U.S. Pat. No. 7,481,105 discloses a tank system with a fuel level gage that includes a measuring pipe in an enveloping element. The measuring pipe includes an ultrasound fuel level sensor that measures the fuel height in the pipe by the propagation time of an ultrasound signal emitted by the sensor and reflected back from the fuel surface.